Portable food heater

ABSTRACT

In one aspect, the present invention provides a consumer appliance that uses RF energy to heat foods stored in a container that is suitable for RF heating.

The present application is a continuation application of U.S.application Ser. No. 11/846,145, filed Aug. 28, 2007, projected to issueas U.S. Pat. No. 7,804,045, which claims the benefit of U.S. ProvisionalPatent Application No. 60/840,463, filed on Aug. 28, 2006, which areincorporated herein by this reference.

BACKGROUND

1. Field of the Invention

The present invention relates to systems and methods for heating foods.As used herein, the term “food” is intended to be interpreted broadly toinclude any consumable in solid, liquid or other form.

2. Discussion of the Background

Consumers have found it desirable to have a small and economicalappliance that can quickly and efficiently heat consumer foods (e.g.,food packed in water or other liquid, coffee, tea, soups, or otherfoods). The device should be easy to use, safe and reliable.

SUMMARY

The present invention provides systems and methods for heating food.

In one aspect, the present invention provides a small appliance forheating foods with high water content that are packaged in containerssuitable for radio-frequency (RF) induction heating. In someembodiments, the appliance is configured to plug into an automotivepower socket (e.g., cigarette lighter socket).

In one embodiment, the appliance includes: a generally cylindricalhousing having an opening formed in a top portion of the housing forreceiving food; a radio-frequency (RF) heating element housed in thehousing and at least partially surrounding the opening; a generallycylindrical base member connected to or integral with a bottom portionof the housing, the base member being configured to fit into aconventional automobile cup holder; an RF power circuit configured toprovide RF power to the RF heating element, the RF power circuit beinghoused in the housing and/or the base member; and a power plugelectrically coupled to the RF power circuit, the power plug beingconfigured to mate with an automotive power socket. In some embodiments,the RF heating element is a coil. In some embodiments the appliancefurther includes a user interface for enabling a user of the portablefood heater to select one of a heat option and a warm option. In someembodiments, the base member may include cooling vents and the RF powercircuit includes an oscillator; an RF power generator coupled to theoscillator; and a controller configured to control the oscillator.

In another aspect, the invention provides a food heating method. In oneembodiment, the method includes: obtaining a portable food heater,wherein the portable food heater comprises: a generally cylindricalhousing having an opening formed in a top portion of the housing forreceiving food; a radio-frequency (RF) heating element housed in thehousing and at least partially surrounding the opening; a generallycylindrical base member connected to or integral with a bottom portionof the housing; an RF power circuit configured to provide RF power tothe RF heating element, the RF power circuit being housed in the housingand/or the base member; and a power plug electrically coupled to the RFpower circuit; placing the base member of the portable food heater intoa cup holder of a car, the car having a power socket configured toreceive a power plug; plugging the power plug into the power socket;placing food in the opening; and after plugging in the power plug andafter placing the food in the opening, activating the portable foodheater such that the RF power circuit provides a sufficient amount of RFpower to the RF heating element to cause the food to heat.

The above and other embodiments of the present invention are describedbelow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments of the presentinvention. In the drawings, like reference numbers indicate identical orfunctionally similar elements.

FIG. 1. illustrates an appliance according to one embodiment of theinvention.

FIG. 2 illustrates a cavity surrounded by an induction heating element.

FIG. 3 is a functional diagram of an appliance according to oneembodiment of the invention.

FIGS. 4A-4B illustrate an appliance according to another embodiment ofthe invention.

FIG. 5 is a simplified circuit schematic of various components of anappliance according to an embodiment of the invention.

FIG. 6 shows a modeled waveform.

FIG. 7 is a flow chart illustrating a process according to oneembodiment.

FIG. 8 illustrates an appliance according to a second embodiment of theinvention.

FIG. 9 further illustrates the appliance according to the secondembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, the words “a” and “an” mean “one or more.”

FIG. 1 illustrates an appliance 100, according to one embodiment of theinvention, for heating foods. Appliance 100 includes a housing 101, aplug 102 for plugging into a standard 110VAC outlet, a suitable exposedcavity 104 for receiving a container 105 (e.g., a magnetic steelcontainer) containing food that the user of appliance 100 desires toheat, and a user interface 106, which may include buttons and or knobsor other control devices that enable a user of appliance 100 to operatethe appliance.

Appliance 100 may be air cooled and include all safety features forensuring safe product delivery by suitably controlling product endtemperature. Appliance 100 can be a stand alone device or its salientfeatures integrated into a larger appliance such as a cooktop or ovenrange. In some embodiments, appliance 100 is a countertop appliance thatis sized such that is sit fit on most any kitchen countertop. Forexample, appliance 100 may be the size of a conventional toaster.

Cavity 104 is further illustrated in FIG. 2. As illustrated in FIG. 2,in some embodiments, appliance 100 includes a radio-frequency (RF)heating element 202 (e.g., an induction coil 202, such as a copper coil,in the embodiment shown) that is housed within housing 101 and that isconfigure to be in close proximity to cavity 104. In the embodimentshown, heating element 202 is in the shape of a coil and surrounds orpartially surrounds the cavity 104.

Heating element is configured to produce a varying magnetic field whenan alternating current passes through element 202. When container 105 isexposed to the varying magnetic field, electrical currents (e.g., eddycurrents) are induced in container 105. These induced currents increasethe temperature of container 105, and this heat that is produced is usedto heat the food in the container. In some embodiments, for user safetyreasons, heating element 202 is physically and electrically isolated,thereby preventing direct consumer access.

Referring now to FIG. 3, FIG. 3 is a functional diagram of appliance 100according to one embodiment. As illustrated in FIG. 3, element 202 maybe coupled to an RF power generator 302 and to a rectifier circuit 310,and may be connected in parallel with a capacitor 304. Rectifier 310 maybe connected to an AC power source 312 (e.g., via plug 102) and may beconfigured to rectify the AC power provided by power source 312. Powergenerator 302 may be coupled to an oscillator 306 that provides an RFsignal to power generator 302, which functions to amplify the RF signal.

Oscillator 306 may be coupled to a control module 308, which may beconfigured to control the frequency, amplitude and/or duty cycle of theRF signal generated by oscillator 306, and thereby control the RF powerdelivered to container 105. In some embodiments, to prevent undesirableheating stratification or damage to container 105, controller 308 isconfigured to ensure that the RF power delivered to container 105depends on the characteristics of container 105 and/or the foodcontained therein. In some embodiments, other means of RF generation maybe used that do not include an RF oscillator, such as a controlled ordynamically responsive form of a relaxation oscillator.

As also shown in FIG. 3, one or more sensors (e.g., sensors 314-317) maybe disposed adjacent or within cavity 102. The sensors may include a“container presence” detector 314 for detecting the presence of acontainer with cavity 104, a temperature sensor 315 to monitor thetemperature of container 105 and/or the food therein, an optical reader316 (e.g., a bar code reader) for reading indicia (e.g., a bar code orother marking) located on an outer surface of container 105 (e.g., thebottom of container 105), a weight measuring device 317.

As further shown in FIG. 3, appliance 100 may include suitable usercontrols 340 to allow the user to select or adjust heating profiles(e.g., power level and power delivery duration).

In practice, a user places a compatible (e.g., steel) container 105 offood in the provided cavity 104 and presses a button (e.g., a “Start”button), which causes controller 308 to use heating element 202 tocreate the RF energy used to heat the container, and, thereby, the food.A Magnetic steel container can be used to improve efficiency withadditional effect of hysteretic heating. Controller 308 may be“intelligent” (i.e., controlled by software) and, therefore, can beconfigured to employ a number of methods to ensure that the food issafely and effectively heated. Some methods to guarantee food-specificheating may employ bar coding, container color coding and/or a userinterface.

Container Presence Detection

In some embodiments, appliance 100 senses whether a suitable container105 has been properly placed in cavity 104 before initiating the desiredheat cycle (i.e., before producing the RF energy needed to heat thefood). It may be important to detect whether a suitable container 105has been inserted into cavity 104 before allowing a heating cycle tobegin. Failure to do so could allow appliance 100 to be improperly usedand create a potential fire/high temperature hazard. A number of methodsfor detecting the presence of a container 105 are contemplated.

One sensing method could employ circuitry that senses a change in theoperation the RF power switching device operation relative to a normalcontainer presence. A sensed change could disable the heating cycle,protecting the user from RF power and the appliance from incorrectoperation. Detecting the presence of a container 105 may be accomplishedby detecting the difference between a no-load resonant frequency and aloaded resonant frequency. For example, when a container 105 is notpresent within cavity 104, the resonant frequency of the appliance'stank circuit 399 (see FIG. 3) frequency is lower than when the container105 is located in cavity 104. Detecting the presence of a container 105may also be accomplished by detecting the amount of current flowingthrough coil 202. When a container 105 is not present in cavity 104,less current is drawn than when the container 105 is present in cavity104. In both cases, the frequency and current draw can be characterizedfor a container present or not.

Another method (not requiring extra sensors) is to sense the impedanceof the RF circuit. In a parallel resonant circuit, the impedancedecreases with an increasing effective load in the coil—this isparticularly true when the load is well coupled. An excellent example ofa well coupled load is a magnetic steel container in close proximity tothe RF coil. If the impedance is sensed as being too high (no containeror other unintended foreign part), generation of the RF field can beprohibited.

Another sensing method is to use a light source (such as an LED) and apaired sensor. When properly designed, the detected presence, absence orattenuation of a scattered or direct light can be sensed by a receiverand used to determine the presence or absence of a container. The methodused can include a source that provides a continuous output on demandor, for more immunity to ambient light, modulated output. When theoutput is modulated, the sensor can synchronously detect presence orabsence of the (light) signal with high accuracy.

A reflective sensor pair, consisting of a source whose beam is reflectedoff the container to be sensed along with a sensor that is used todetect the reflected output signal, can also be used to determinewhether a container is present in the appliance. Reflected sensors aregenerally provided as matched pairs and even sometimes integrated into asingle package. In any case, the sensor must be properly located tosense the reflected light from the emitter source. The emitter can senda continuous signal on demand or be modulated and detected as describedin the above transmissive method.

Suitable Container Detection

In addition to detecting the presence or absence of a container withincavity 104, it may be useful to detect whether a present container issuitable or intended for induction heating. For example, an improperlyfilled container may appear to meet the requirements of containerpresence, but would be unsuitable because heating such a container couldbe inappropriate and potentially hazardous. A number of methods fordetecting whether a container placed in cavity 104 is suitable and/orintended for induction heating are contemplated.

In some embodiments, the method employs weight measuring device 317(e.g., a spring/contact, piezoelectric sensor, strain gauge, or otherweight measuring device) (which also may be used in determining whethera container is present). In some of these embodiments, controller 108may be configured to (1) read data provided by sensor 317, which dataprovides information as to the weight of the object placed in cavity 104and (2) determine whether the weight of the object falls within apredetermined weight range (e.g., more than 8 ounces). If the objectdoes not fall within the predetermined weight range, then the controllerwill deem the object to be unsuitable and controller 108 may beprogrammed to ignore requests from the user to heat the unsuitableobject and/or cause an error message to be displayed to the user.Alternatively or in addition to the above, controller 108 may beconfigured to set the amount of energy delivered to the object based, atleast in part, on the data read from device 317.

In some embodiments, the method employs the above mentioned circuitrythat senses whether the RF power generator 302 is operating withinpredetermined operating parameters and/or sensing the impedance of the“load” seen by power generator 302.

In some embodiments, the method employs optical reader 316, which may beexposed to the user or may be internal to appliance 100. In theseembodiments, a suitable container may be a container that not only meetsa certain weight requirement but also has certain indicia located on anouter surface of the container that can be read by reader 316. Forexample, in embodiments where the reader 316 is exposed to the user, inorder for the user to heat the food in a particular container, the usermust first position the container so that reader 316 can read a barcodeon the container (thus, if the container does not have a bar code, then,in some embodiments, user can't use appliance 100 to heat thecontainer). After reader 316 reads the barcode, it provides tocontroller 308 data encoded in the barcode. Controller 308 thendetermines whether the container may be heated, where the determinationis based, at least in part, on the provided data. If controller 308determines that the container may not be heated, controller 308 maycause an error message to be displayed to the user, otherwise controller308 may prompt user to place the container in cavity 104.

In embodiments where reader 316 is internal to appliance 100, reader 316is positioned such that after a user places a container with a barcodein cavity 104, reader 316 can read the barcode, provided the barcode isoriented properly. After reader 316 reads the barcode, it provides tocontroller 308 data encoded in the barcode. Controller 308 thendetermines whether the container may be heated, where the determinationis based, at least in part, on the provided data. In some embodiments,the bar code may extend all the way around container 105 so that nomatter which way container 105 faces, the bar code can be read by thereader.

In some embodiments, if the barcode is not orientated properly relativeto reader 316, appliance 100 may automatically move the container so asto properly align the barcode relative to reader 316. For example,appliance 100 may have a rotating device (not shown) for rotating thecontainer around its longitudinal axis. In these embodiments, it may beadvantageous to put the barcode (or other indicia) on the bottom of thecontainer and position reader 316 adjacent the bottom of cavity 104 andlooking up towards the top of the cavity 104.

In some embodiments, the method for detecting whether the container issuitable and/or intended for induction heating employs a transponder(e.g., an RF identification (RFID) tag or the like) that is attached tothe container (e.g., the container may have a built-in RFID tag). Forexample, the transponder may be attached to the container and covered bya label that is affixed to the container or it may be attached to orwithin a false bottom of the container. The RF heating element 202 maybe used to supply power to the transponder and to communicate with thetransponder. In some embodiments, in response to receiving power, thetransponder transmits data. The data could include productidentification information as well as a heating profile and/or aspecified energy to be delivered in heating the container. Thecontroller 308 may use this information to control the heating of thecontainer.

Temperature Detection

While appliance 100 is heating a suitable container 105, it may bebeneficial to detect and monitor the temperature of container 105. Whiletemperature sensing may provide the potential for temperature control,it also provides protection against the potential hazard of overheating.

Container overheating could occur if appliance 100 is improperly used toheat an empty, or partially empty, container, re-heat a previouslyheated container or heat a foreign conductive substance. To provideproper protection or control, the portion of the container with thehighest heat transition potential is preferably monitored. The topportion of container 105 appears to be the best candidate.

In order for the heating element 202 to efficiently magnetically coupleto container 105, heating element 202 should be in close proximity tocontainer 105. Accordingly, temperature sensor 315 may be embedded in orattached to heating element 202. Also, as discussed above, because itmay be advantageous to monitor the top portion of container 105, sensor315 may be disposed adjacent this portion of container 105.

Usually, it is difficult to obtain a proper temperature reading ofcontainer 105 if temperature sensor 315 is in close proximity to heatingelement 202 when element 202 is being used to generate the RF field usedto heat container 105. This is due to the impact that the RF energy hason most sensors. Because one RF heating methods contemplated relies onthe high frequency RF field being modulated at twice (2×) the ACfrequency, there are recurring instances when no field is present. Theseinstances occur at every half cycle when the AC line voltage swingsthrough 0V. Accordingly, in one embodiment, temperature sensor 315and/or controller 308 is synchronized with this recurring event toobtain a reading since the field will not exist to interfere with thereading. That is, controller 308 may be programmed to read the output oftemperature sensor 308 at the specific instances in time when no RFfield is present.

Temperature detection methods can also include direct contactmeasurement where sensor 315 is placed such that sensor 315 is in directcontact with container 105 at least when container 105 is being heated.One way this can be accomplished is by disposing sensor 315 on a lid 122that is designed and configured such that, when in a closed position,the lid 122 covers cavity 104 and causes sensor 315 to contact the topportion of container 105 and requiring the user to close lid 122 beforeheating can being (e.g., the sensor could be attached to the inside oflid 122). Examples of direct contact sensors include semiconductor(temperature sensors or simple ΔV_(be) of a transistor), thermocouple(dissimilar metal or Siebeck effect) RTD (resistance Temperaturedevice), NTC or PTC (Negative and Positive Temperature Coefficient)devices whose resistance change with temperature.

Additional detection can include a combination approach. Thus, one ormore temperature sensors 315 may be employed. Additionally, should atransponder be used for product identification or other purposes (e.g.,as described above), the same transponder could include or couple to atemperature sensor and transmit the measured temperature.

Another temperature technique that may be used is to include a liquidcrystal temperature monitor on the can. Such devices may change theirappearance with a threshold temperature is reached. Such a device couldbe optically monitored with an inexpensive light source and sensor, as anon-contact technique. This same temperature monitor could then functionas a warning indicator to the consumer who would see the monitor anddetermine based on the color of the monitor whether the product is hot.

Energy Selection

The amount of energy delivered to container 105 by appliance 100 inresponse to the user initiating the heating of container 105 (e.g., byinserting a suitable container into cavity 104, by pressing a “start”button, etc.) may be set automatically by controller 308 in advance of,or in response to, the user initiating the heating or set manually bythe user. A number of methods for automatically selecting the amount ofenergy are contemplated.

In some embodiments, the automatic selection method employs opticalreader 316. In these embodiments, indicia may be located on an outersurface of container 105 so that reader 316 can “read” the indicia(either when the user manually positions the indicia in the field ofview of reader 316 or when the user places the container in cavity 104).In response to reading the indicia, reader may output to controller 108data corresponding to the indicia. Encoded in the indicia may be aproduct identifier, a power level identifier and/or a heating durationidentifier. If only a product identifier is encoded, then controller 308may use the product identifier and a lookup-table to determine theappropriate power level and duration settings (i.e., for each productidentifier included in the table, the table associates a power/durationsetting with the identifier).

Alternative Embodiment

Referring now to FIGS. 4A-B, FIGS. 4A-B illustrate an appliance 400according to another embodiment of the invention. In some embodiments,appliance 400 is identical to appliance 100 in substantive respect, butwith the exception that cavity 104 is contained in a door 402. In theembodiment shown, door 402 moves between an open position (see FIG. 4A)and a closed position (see FIG. 4B). Door 402 may be configured to pivotbetween its open position and closed position, as is shown in FIGS.4A,B. But in other embodiments, door 402 may be slideable between itsopen and closed position so that the door can be slid open and closedlike a drawer.

When door 402 is in the open position, cavity 104 is exposed, therebyenabling a user to insert a container into cavity 104. When door 420 isin the closed position, cavity 104 is not exposed, thereby preventingthe user from inserting or removing an object from cavity 104.

In embodiments where appliance 400 includes reader 316 and the user isrequired to position indicia on a container in the field of view ofreader 316 in order to heat the food stored in the container, controller308 may be configured to automatically open door 402 in response toreader 316 reading the indicia and controller 308 confirming that thecontainer is a suitable container based on an output from reader 316.

Also, in embodiments where appliance 400 includes a means for detectingthe presence of a container within cavity 104, controller 308 may beconfigured to automatically close door 402 in response to the detectionof a container in cavity 104. In some embodiments, for safety,controller 308 activates power generator 302 only after a suitablecontainer is disposed in cavity and door 402 is closed.

Referring now to FIG. 5, FIG. 5 is a simplified circuit schematic ofvarious components of appliance 100, 400. The circuit shown is a poweroscillator design that provides efficient power transfer to container105. In this embodiment, power switches M1, M2 are driven at just under70 kHz through R2, R8 with a controlled input waveform V3.

Container 105 is modeled as power resistor R5. Heating element L3 andcapacitor C3 provide a resonant circuit. The DC resistance of element L3is shown as resistor R7.

Diodes D1-D4 comprise the AC line rectifier 310 and provide virtuallyunfiltered rectified voltage to the RF oscillator. Capacitor C4 providesa low impedance at RF frequencies. Its value is also chosen so that itsreactance at line frequency is small providing the circuit with a powerfactor very close to 1.

Effective heating has been shown to occur at RF frequencies between 45kHz and 120 kHz but other frequencies may be employed. The resonantheating system can either be self oscillating or driven by an adaptiveoscillator providing very efficient operation.

From an RF power transfer stance, operation relies on a known load(container) being placed in the coil. With the employed high couplingefficiency of the coil/container, the circuit Q is very low and in therealm of approximately 2-4. When a part is coupled this tightly, poweris transmitted predictably. Stray fields are minimized and generallyeasy to control. Variations in operating frequency minimally impactpower transfer.

Actual power level control is provided by enabling/disabling RFgeneration at the start of each 50/60 Hz half cycle (AC line zerovoltage crossing). Higher power output and therefore increased heating,requires the RF generator to be enabled during a higher number 50/60 Hzcycles. Lower power requires RF to be enabled during fewer cycles. Thistechnique has the added advantage of easier control and beginning eachRF envelope at low voltage, minimizing excessive line current spikes andconducted radiation.

Efficient operation occurs because the power switching device (e.g.,MOSFET) is operated ZVS (Zero Voltage Switching) in the preferredembodiment, however turning off does not occur at zero current. Amodeled waveform is shown in FIG. 6.

Referring to FIG. 6, notice the MOSFET power switch drain-source Voltage(502) is nearly zero before the gate voltage (504) is applied. Currentthrough the MOSFET is shown (506) and reaches a known (predetermined)peak when the gate voltage is removed. The drain-source voltage may beused as a sensor for this current. During the first interval where thepower switch is turned on, the drain current is increasing, so themagnetic field generated by coil L3 is increasing (changing) andimparting energy to the container. In the following interval, the switchis turned off and the coil field collapses—the changing coil field againimparts power to the container. Circuitry is designed to turn on thepower switch (MOSFET) as soon as the drain voltage returns to nearlyzero, maintaining an efficient method of switching.

Referring now to FIG. 7, FIG. 7 is a flow chart illustrating a potentialprocess 700 for heating food stored in a container using an applianceaccording to one embodiment of the invention.

Process 700 may begin in step 702, where a user of the appliancepositions the container so that a barcode on the container is in thefield of view of the appliance's barcode reader. In step 702, the readerreads the barcode and outputs the read code (or portion thereof) to theappliance's controller. In step 704, the controller 704 uses the datareceived from the reader to determine whether or not to allow the userto heat the container. If the controller decides to allow heating, thenthe process proceeds to step 708, otherwise the controller causes anerror message to be displayed on the appliance's display (step 706).

In step 708, controller causes the appliance's door to automaticallyopen, thereby exposing the container receiving cavity. In step 710, theuser inserts the container into the cavity. In step 712, after thecontainer is inserted into the cavity, the controller determines theweight of the container. In step 714, controller determines whether theweight falls within a predetermined range (e.g., is the weight over 8ounces). If not, process 700 may proceed to step 706, otherwise process700 may proceed to step 716. In step 716, the controller determines theamount of energy to provide to the container. This selection may bebased on: user input, data output from reader and/or the determinedweight of the container. In step 718, controller operates theappliance's RF power generator, thereby causing the appliances heatingelement to generate a varying magnetic field, which varying fieldinduces currents in the container, which currents create heat that istransferred to the food in the container. In step 720, while energy isprovided to the container, the controller reads the output of atemperature sensor to determine the temperature of the container. Instep 722, the controller determines whether the determined temperatureis within a predetermined range (e.g., less than X degrees Fahrenheit).If not, the controller causes the appliance to cease providing energy tothe container (step 724), otherwise the appliance continues to provideenergy to the container until the desired amount of energy has beenprovided.

After the end of the heat cycle, the door may automatically open so thatthe user can retrieve the container. After retrieving the container, theuser may wish to shake the container because there is a chance thetemperature of the food is not uniform and shaking the container improvethe likelihood that the temperature will be uniform when the user wantsto consume (e.g., drink) the food.

Referring now to FIG. 8, FIG. 8 is a schematic illustrating an appliance800 according to another embodiment of the invention. As illustrated,appliance 800 is in the form of a coffee mug and is portable. That is,appliance 800 includes a generally cylindrical housing 802 that isclosed at the bottom and open at the top, thereby forming an opening 890for receiving food.

Referring now to FIG. 9, FIG. 9 is a cross-sectional illustration ofappliance 800. As illustrated in FIG. 9, housing 802 houses RF heatingelement 202, which is coupled to an RF power circuit 902 that isconfigured to provide RF power to RF heating element 202. Heatingelement 202 may be in the form of a coil and the coil may surround aportion of opening 890, as illustrated in FIG. 9. Food (e.g., abeverage) may be placed directly in opening 890 or the food may beenclosed in a can or other container, which is placed in opening 890.

Heating element 202 is used to generate an RF field, which field is usedto inductively heat the food placed in opening 890 and/or inductivelyheat a container placed in opening 890 that contains the food. Morespecifically, in some embodiments, when RF power circuit 902 provides RFpower to element 202 an RF electromagnetic radiation is generated byelement 202, which radiation may be used to induce currents in asuitable container (e.g., a magnetic steel container) placed in opening890. Power circuit 902 may include elements 302, 304, 306, 308 and/or310, arranged as shown in FIG. 3.

As sown in FIG. 9, in one embodiment, power circuit 902 is housed in abase member 804 of appliance 800. However, in other embodiments, powercircuit 902 may be housed in housing 802, while in still otherembodiments, some components of circuit 902 are housed in housing 802while the remaining components are housed in base 804. In someembodiments, power circuit 902 is designed to receive its power from,for example, a power source in a vehicle (e.g., a battery). Thus,appliance 800 may include a plug 801 (see FIG. 8) for receiving powerfrom a power source in a car. For example, plug 801 may mate with anautomotive power socket (e.g., cigarette lighter socket).

Referring back to FIG. 8, housing 802, in one embodiment, sits atopcylindrical base member 804. Housing 802 and cylindrical base member 804may be separate pieces that have been attached together or they may beintegral (e.g., formed from a single piece or mold). In someembodiments, base member 804 has an outer diameter that is less than theouter diameter of housing 802, thereby enabling base member 804 to fitinto a cup-holder 817. Base member 804 may be tapered to facilitateinsertion into cup-holder 817. As also shown, base member may includeair vents 806 for cooling circuitry (e.g., generator 302) that may behoused in base member 804 and/or housing 802. Additionally, an end 808of base member 804 (e.g., the end that is inserted into cup-holder 817)may be weighted to prevent appliance 800 from tipping over when it is inan upright position.

A person who spends a large amount of time in a vehicle may findappliance 800 quite useful as it enables the person to heat foods whilethe person is in the vehicle. Preferably, to facilitate consumeracceptance, appliance should be simple to use. Accordingly, in someembodiments, appliance has only a minimal number of buttons or nobuttons at all. For example, in some embodiments, appliance 800 includesa sensor 990 (see FIG. 9) for determining that food has been placed inthe opening 890 and, in response to sensor 990 detecting this event,appliance 800 automatically begins providing RF power to element 202 to,thereby, heat the food.

In some embodiments, appliance may have a heat mode and a keep warm mode(in this embodiment hosing 802 may have two buttons thereon—one toactivate the heat mode and the other to activate the keep warm mode—or aswitch to switch between the two modes—or other user interface elementto enable the user to select the desired mode). In the heat mode, agreater amount of power is provided to the coil than in the keep warmmode. Thus, if a person already has hot food, the person can put thefood into opening 890 and select the keep warm mode to keep the foodwarm and conserve power.

Appliance 800 may include any or all of the safety features (e.g.,sensors 314 and 317 and reader 316) described above with reference toappliance 100.

While various embodiments/variations of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Thus, the breadth and scopeof the present invention should not be limited by any of theabove-described exemplary embodiments.

Additionally, while the process described above and illustrated in thedrawing is shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, and the order of the steps maybe re-arranged.

What is claimed is:
 1. A portable food heater, comprising: a generallycylindrical housing having an opening formed in a top portion of thehousing for receiving food; a radio-frequency (RF) heating elementhoused in the housing and at least partially surrounding the opening; agenerally cylindrical base member connected to or integral with a bottomportion of said housing, said base member being configured to fit into aconventional automobile cup holder; an RF power circuit configured toprovide RF power to the RF heating element, said RF power circuit beinghoused in said housing and/or said base member; and a power plugelectrically coupled to the RF power circuit, said power plug beingconfigured to mate with an automotive power socket.
 2. The portable foodheater of claim 1, wherein the RF power circuit that is housed in saidhousing and/or said base member comprises: an oscillator for generatingan RF signal; and a power amplifier for receiving and amplifying the RFsignal, wherein the RF heating element is coupled to an output of thepower amplifier.
 3. The portable food heater of claim 1, wherein thebase member has an outer diameter that is less than an outer diameter ofthe housing.
 4. The portable food heater of claim 1, wherein at least aportion of the RF power circuit is housed in the base member, and thebase member includes air vents for cooling said at least a portion ofthe RF power circuit housed in the base member.
 5. The portable foodheater of claim 1, wherein the portable food heater is operable tooperate in a heating mode, and the portable food heater is also operableto operate in a warming mode, wherein when the portable food heater isoperating in the heating mode, the RF power circuit is configured toprovide a first amount of power to the RF heating element, when theportable food heater is operating in the warming mode, the RF powercircuit is configured to provide a second amount of power to the RFheating element, and the second amount of power is less than the firstamount of power.
 6. The portable food heater of claim 5, wherein theportable food header has a means for enabling a user to select betweenthe heating mode or the warming mode.